(a) Field of the Invention
The present invention relates to an injector for a diesel engine. More particularly, the present invention relates to an injector for a diesel engine that controls the injecting angle of fuel in accordance with a driving type of the diesel engine.
(b) Description of the Related Art
Due to exhaust gas regulations for diesel engine vehicles, diesel engine designers are developing a diesel engine in which fuel is burned by a new combustion method, often referred to as a homogeneous charge compressed ignition (HCCI) engine. With reference to the accompanying drawings, the concept of the HCCI engine will hereinafter be described in detail.
FIG. 7 is a graph showing average effective pressure and driving type based on an engine speed according to an HCCI engine. As shown in FIG. 7, according to the HCCI engine, a fuel is burned by an HCCI combustion method under a part load condition where a large quantity of exhaust gas is generated, and is burned by a conventional diesel combustion method under a full load condition where high power is needed. In other words, as shown in FIG. 8A, the fuel is injected into a chamber with a wide injecting angle (about 150-160°) under the part load condition. In contrast, the fuel is injected into the chamber with a narrow injecting angle (about 60-70°) under the full load condition, as shown in FIG. 8B.
FIG. 9 is a figure showing analysis results at injection and combustion processes of a fuel. A fuel is injected into a chamber at a top dead center (TDC) according to the conventional diesel combustion method. The injected fuel is mixed and simultaneously burned. Therefore, the fuel may not be sufficiently mixed and an incomplete combustion may partially occur. Therefore, smoke may occur in the combustion process, and exhaust gases may increase. Such an increase of exhaust gas is an innate drawback of the conventional diesel combustion method.
On the other hand, in the HCCI combustion method, the fuel is injected at 60-100° at a back top dead center (BTDC) in order to ensure a sufficient mixing time of the fuel
However, if the fuel is injected with the injecting angle of the conventional diesel engine injector (about 150-160°) at the 60-100° BTDC, the injected fuel is adhered to a cylinder wall since inner pressure of the cylinder is very low. Accordingly, exhaust gases, such as smoke and HC, may increase. Therefore, an injector that has a smaller injecting angle (about 60-70°) is required to be used according to the HCCI combustion method where the fuel is injected at the 60-100° BTDC.
However, high power may not be generated according to the HCCI combustion method, and thus, the HCCI combustion method cannot be used for entire driving conditions of an engine.
To solve such problems, a diesel injector of a complex combustion method where the diesel combustion method is used together with the HCCI combustion method has been developed. According to the diesel injector of the complex combustion method, an injection hole that has a wide injecting angle and an injection hole that has a narrow injecting angle are formed in two rows, and a lifting amount of a needle is controlled so as to control the combustion method.
However, if the injection holes are formed in two rows, fuel can leak through the lower injection hole when the fuel is injected through the upper injection hole. Therefore, the injecting pressure of the fuel at the upper injection hole may be lowered.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.